Tool-change system for a machine tool with a number of machining heads

ABSTRACT

The tools of the various machining heads are housed on a common drum, which is remote from the heads and rotated to select a given row of tools. At each head, there is provided an intermediate station having a container housing a row of tools; and a shuttle provides for sequentially transferring the tools between the drum and the intermediate stations. Each container is rotated 90° between a position cooperating with the shuttle and a position cooperating with a device for exchanging the tools between the head and the container. The container is also movable with respect to the device to select the location of the tool to be changed.

BACKGROUND OF THE INVENTION

The present invention relates to a tool-change system for a machine toolwith a number of machining heads, in particular for machining printedcircuit boards.

Various tool-change systems are known for machine tools of the abovetype, each machining head of which normally has a respective tool storeand a respective device for exchanging tools between the store and thehead. In one known machine, the various stores are located on themachine bed, and the worktable carries a number of tool-change devices.

In another known machine, each head is provided with a drum supporting anumber of rows of tools, and which rotates selectively on the machinebed to present the tool-change device with the row containing therequired tool. In this case, too, the tool-change device is carried onthe table.

The tool-change systems of the above known machines have severaldrawbacks. In particular, they call for a number of identical membersfor supporting and selecting the tools, thus increasing the cost of themachine. Moreover, they occupy considerable space on the machine bed,thus enormously increasing the size of the machine. And finally, tochange the tool stores, the machine must be arrested, thus alsoincreasing the running cost of the machine.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a highlystraightforward, reliable tool-change system for a machine tool with anumber of machining heads, designed to eliminate the aforementioneddrawbacks typically associated with known systems.

According to the present invention, there is provided a tool-changesystem for a machine tool with a number of machining heads, inparticular for machining printed circuit boards; characterized in thatthe tools for said heads are housed in a common store, and aretransferred selectively between said store and a group of intermediatestations; changing means being provided to change the used tool on eachhead with a tool transferred to one of said stations.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the invention will be describedby way of example with reference to the accompanying drawings, in which:

FIG. 1 shows a partial front view of a machine tool for machiningprinted circuit boards, and incorporating a tool-change system inaccordance with the present invention;

FIG. 2 shows a partial larger-scale side view of the FIG. 1 machine;

FIG. 3 shows a larger-scale detail of FIG. 1;

FIG. 4 shows a partial section along line IV--IV in FIG. 2;

FIG. 5 shows a much larger-scale detail of FIG. 1;

FIG. 6 shows a left-side view of the FIG. 5 detail;

FIG. 7 shows a larger-scale section along line VII--VII in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Number 10 in FIG. 1 indicates as a whole a machine tool for machiningprinted circuit boards, and which comprises a bed 11 supporting twolateral uprights 13, only the left-hand one of which is shown in thedrawings. Uprights 13 are fitted with a steel crosspiece 14 comprising ahorizontal plate 16 and two vertical plates 17 (see also FIG. 2); andmachine 10 also comprises a worktable 18 movable in known manner in afirst direction hereinafter referred to as axis Y.

A carriage 44 travels along crosspiece 14 in a second directionhereinafter referred to as axis X, and comprises two parallel bars 46connected to each other by a number of crosspieces 47. Each bar 46 is asteel box bar, and is reinforced by a pair of rectangular-section bars45 and 50; each pair of bars 45, 50 is fitted with a respective row ofmachining heads 33, e.g. comprising four heads 33; each twocorresponding heads in the two rows form a pair of heads 33, so thatcarriage 44 carries a total of eight heads 33; and each head 33comprises a vertical tool-holder spindle 34 for receiving a tool 36, andwhich is moved along a vertical axis Z by a reversible numeric-controlelectric motor (not shown).

Machining of the printed circuit boards mainly comprises drilling, butmay also comprise milling operations. The boards are arranged in packs,each of which is placed for machining on a fixture 38 fitted to table 18and associated with a respective head 33. Table 18 therefore carrieseight fixtures 38 arranged in two rows, with a gap 42 between adjacentpairs of fixtures 38.

The first pair of fixtures 38 on the left is flanked by a first pair ofdevices 43 for changing tool 36, each device being associated with arespective head 33 in the corresponding pair; each of the spaces 42between pairs of fixtures 38 houses a respective pair of devices 43associated with heads 33 in the next pair to the right; each device 43is defined by a pneumatic gripper 40 for removing a tool 36, e.g. fromspindle 34; and gripper 40 is moved along the Z axis in known manner bya corresponding pneumatic piston (not shown).

According to the invention, the system for changing tools 36 comprises astore 51 (indicated by a dash line in FIG. 1 for the sake of simplicity)which is common to tools 36 of all of heads 33 and is located outwardsof crosspiece 14. More specifically, store 51 (FIGS. 2 and 4) is fittedto a support indicated as a whole by 52, and which in turn is fitted tothe left-hand upright 13 and comprises a bracket 53 extending forwardsand having a vertical wall 54 fitted with a rotary shaft 56 parallel tocrosspiece 14.

Store 51 is defined by a drum 57 fittable removably to shaft 56substantially as described in European Patent N. 541.020. Morespecifically, drum 57 houses a number of--e.g. twenty--rows of tools 36;each row is located in a predetermined angular position on drum 57, andmay receive three clips or strips 58 of tools 36, so that store 51 has acapacity for an extremely large number of tools 36.

Each strip 58, in itself known, is defined by a body made of plasticmaterial and having a number of locations or seats for tools 36, e.g. ofthe collarless type. Each tool 36 is retained frictionally inside therespective seat by elastic elements on the body of strip 58, and iswithdrawn from and inserted inside the seat axially. Drum 57 alsocomprises a guard 60 for tools 36.

Wall 54 of bracket 53 is also fitted with an electric step motor 59,which, by means of a belt 61, rotates drum 57 to move the required rowof tools 36 into a transfer position T, in which tools 36 are positionedhorizontally with the tips facing the rear of machine 10. To select therow of tools 36, store 51 is therefore moved in a plane perpendicular tocrosspiece 14.

At each pair of machining heads 33 on carriage 44, an intermediatestation 62 (FIG. 1) is provided for temporarily housing the new tools 36to be fitted to spindle 34 of head 33, and the used tools 36 extractedfrom spindle 34 by tool-change device 43. Each intermediate station 62comprises a container 63 (FIGS. 5 and 6) for housing a predeterminednumber of tools 36 in a row parallel to crosspiece 14. Container 63 isdefined by a body similar to that of strips 58 on drum 57 but normallywith no tools 36, and is fitted to a support 64 integral with a plate 65fitted underneath crosspiece 14.

More specifically, support 64 comprises a guide defined by two prismaticbars 66 (FIG. 7) parallel to crosspiece 14 and between which container63 is housed in sliding manner. Bars 66 have a median plane Mperpendicular to the axes of tools 36, and are connected to each otherby two sides 67, each having a pin 68. Support 64 comprises two sides 69to which the two pins 68 are fitted in rotary manner; and, in the FIG. 7position, the axis of pins 68 is below the median plane N of bars 66.

An appendix 70 of support 64 is fitted with a pneumatic motor 71 havinga shaft 72, which is rotated between two positions at 90° to each other,and is connected by a joint 73 to the adjacent pin 68, so that bars 66are rotated 90° together with container 63. Bars 66 are normally sopositioned by motor 71 that container 63 positions tools 36 horizontallyand aligned with the row of tools 36 on drum 57 in transfer position T.When rotated 90°, motor 71, by means of bars 66, moves container 63 intoa vertical tool-change position, with the tips of the tools facingdownwards as shown in FIGS. 5 and 7.

A spring 75 is fitted between a pin 80 on support 64 and one end 74 ofcontainer 63, and provides for normally holding container 63 against astop 76 fitted to bars 66. The front rectangular-section bar 45 ofcarriage 44 (FIGS. 1 and 6) is fitted, to the left of respective head33, with a plate 77 supporting an arm 78, which has an appendix 79 forengaging end 74 of container 63.

When container 63 is rotated into the tool-change position, appendix 79draws container 63 parallel to crosspiece 14, in opposition to spring75, to select each time the location of tool 36 to be changed.Conversely, when container 63 is set with tools 36 positionedhorizontally, appendix 79, by virtue of the position of pins 68, failsto encounter bars 66 and therefore travels freely.

The system for changing tools 36 also comprises a transfer deviceindicated as a whole by 81 and which is common to all of intermediatestations 62 and provides for selectively transferring tools 36 betweenstore 51 and intermediate stations 62, which are served sequentially.Device 81 comprises a shuttle 82 fitted to a known linear actuator 83,which extends rightwards substantially the whole length of crosspiece14, and which, leftwards, extends through an opening 80 in upright 13and beyond drum 57.

More specifically, actuator 83 is fitted to crosspiece 14 by supportingmeans comprising an arm 92 (FIGS. 2 and 3) extending outwards of theleft-hand upright 13, and comprises a toothed belt 84 cooperating withvertical-axis pulleys, one of which is rotated selectively by anelectric motor 85. Shuttle 82 comprises a slide 86 fitted to the frontportion of belt 84 and supporting a horizontal guide 87 perpendicular tothe axis of drum 57 to guide a gripper 88 for gripping a tool 36.

Gripper 88 is substantially similar to grippers 40 for changing tools36, is oriented with two movable jaws in a vertical plane, and is movedalong guide 87 by a pneumatic cylinder 89 (FIG. 4) not shown in FIG. 2.The left-hand upright 13 is also fitted with a support 91 fittedremovably with a container 90 for discarded tools 36; and each spindle34 comprises a known tool-condition sensor (not shown) for indicating toa control unit when the respective tool 36 is no longer serviceable dueto damage or wear.

The system for changing tools 36 operates as follows.

To begin with, it is assumed drum 57 (FIG. 4) with tools 36 is fitted toshaft 56; each of spindles 34 is fitted with a tool 36; somealready-used tools 36 are housed inside containers 63 (FIG. 5); andcontainers 63 are set by motor 71 to the angular position shown by thedash line in FIG. 7 and in which the tools are positioned horizontally.

It is also assumed the packs of printed circuit boards for machining arefitted onto fixtures 38 (FIG. 1); machine 10 is performing the setdrilling and milling cycles using the tools 36 in spindles 34; and, ateach cycle, the control unit positions table 18 along axis Y andcarriage 44 along axis X, and then activates spindles 34 of heads 33 tosimultaneously machine the packs of printed circuit boards.

In the course of the above machining cycles, the control unit operatestransfer device 81 to perform a series of transfer cycles of tools 36between drum 57 (FIG. 4) and intermediate stations 62. At each cycle,the transfer of a new tool 36 from drum 57 to intermediate station 62alternates with the return of a used tool 36 from station 62 to drum 57.

To begin with, drum 57 (FIG. 2) is rotated to position the rowcontaining the tool/s 36 to be withdrawn into transfer position T, ifthe row is not already in the transfer position. At the same time,actuator 83 is operated to position shuttle 82, together with gripper88, opposite the tool 36 to be transferred. Pneumatic cylinder 89 (FIG.4) is then operated so that gripper 88 engages tool 36; gripper 88 isclosed; and cylinder 89 is again operated to extract tool 36 from drum57.

Actuator 83 is then operated to position shuttle 82, together withgripper 88, opposite the location in container 63 (FIGS. 1 and 7)associated with the first pair of machining heads 33, into which the newtool 36 is to be inserted; cylinder 89 (FIG. 4) is again operated sothat gripper 88 inserts the new tool 36 inside the selected location;and gripper 88 is then opened and moved by actuator 83 to the locationin container 63 containing the tool 36 to be transferred to drum 57.Whenever possible, the control unit is so programmed that the locationinto which the new tool 36 is inserted is adjacent to that from whichthe used tool 36 is withdrawn.

Once gripper 88 is closed, actuator 83 is operated to position shuttle82, together with gripper 88, opposite the location in the row on drum57 into which the used tool 36 is to be inserted. Operating gripper 88in the same way as before to insert tool 36 inside container 63, theused tool 36 is then inserted inside the respective strip 58 on thedrum.

If a given used tool 36 has been memorized by the control unit as beingno longer serviceable, the control unit arrests actuator 83 and shuttle82 at container 90 (FIG. 1) during the transfer cycle to drum 57, andgripper 88 is opened to drop the discarded tool 36 into container 90.The above transfer cycle is repeated sequentially for all ofintermediate stations 62, and may also be repeated to transfer more thanone tool 36 to each station 62 and so form a standby stock of tools 36in containers 63.

To change tools 36 in spindles 34, operation of transfer device 81 issuspended temporarily. To begin with, the control unit operatespneumatic motors 71 (FIGS. 5 and 7) to rotate bars 66, together withcontainers 63, to position tools 36 vertically; the control unit thenmoves carriage 44 (FIGS. 1 and 2) and table 18 along respective axes Xand Y to align the axes of spindles 34 with grippers 40 for changingtools 36; and grippers 40 are then activated by the pneumatic cylindersto withdraw the respective used tools 36 from spindles 34.

The control unit then moves carriage 44 selectively leftwards so thatappendixes 79 (FIGS. 5 and 6) of arms 78 engage ends 74 of respectivecontainers 63; each container 63 is drawn in opposition to spring 75 toalign the location in container 63 into which the used tool 36 is to beinserted with the gripper 40 (FIG. 1) relative to the front machininghead 33 in each pair; and gripper 40 then inserts the used tool 36inside container 63. The above operation is repeated to insert intocontainers 63 the tools 36 extracted by grippers 40 relative to themachining heads 33 in the rear row.

Two successive operations, similar to those described above, are thenperformed, whereby appendixes 79 position containers 63 to withdraw thenew tools 36 first by grippers 40 of the front row of heads 33, and thenby grippers 40 of the rear row of heads 33. Once carriage 44 and table18 are repositioned, grippers 40 are operated simultaneously to insertthe new tools 36 inside respective spindles 34 and so recommencemachining the packs of printed circuit boards and transferring tools 36between common store 51 and intermediate stations 62.

Drum 57 of tools 36 may be changed by the operator even while the packsof printed circuit boards are being machined, by simply temporarilysuspending transfer of tools 36 by device 81. By virtue of eachcontainer 63 containing a number of tools 36, machine 10, duringreplacement of drum 57, may not only continue working with the tools 36already inserted inside spindles 34, but may also perform severaltool-change cycles between spindles 34 and containers 63.

As compared with known systems, the advantages of the tool-change systemaccording to the invention will be clear from the foregoing description.In particular, common store 51 provides for simplifying the structure ofmachine 10. Moreover, machine 10 is far more compact by eliminating theindividual stores of the various machining heads 33. And finally, usingintermediate stations 62 for tools 36 and a remote common store 51provides for eliminating the downtime incurred on known machine tools tochange the stores, thus reducing the running cost of the machine.

Clearly, changes may be made to the system as described and illustratedherein without, however, departing from the scope of the accompanyingclaims. For example, drum 57 may be replaced by a drawer-type storemoved in known manner in a direction perpendicular to crosspiece 14;machine 10 may comprise only one row of machining heads 33, possiblymovable independently of one another along crosspiece 14; and machine 10may comprise an intermediate station 62 for each head 33, even in thecase of heads 33 arranged in two rows.

Each device 43 for changing tools 36 may provide for serving at leasttwo machining heads 33; container 63 may be fitted to support 64 fortroublefree replacement by hand; and intermediate station 62 maycomprise any number of locations, greater than two, for tools 36, andmay be moved with respect to tool-change grippers 40 by any type ofactuator independent of the movement of carriage 44.

What is claimed is:
 1. A tool-change system for a machine tool with anumber of machining heads for machining printed circuit boards,comprising:a common store for housing tools for said heads, wherein saidtools are transferred selectively between said store and a group ofintermediate stations, changing means being provided to exchange a usedtool on each head with a tool transferred to one of said stations,wherein a common transfer device is provided for transferring the toolssequentially between said store and said stations, wherein each of saidstations houses a predetermined number of tools, means being provided ineach of said stations to select each time the location of the tool to bechanged, wherein said heads are movable along a common guidingcrosspiece, said stations being arranged along at least one line that isparallel to said crosspiece, and said store being located outwards ofsaid crosspiece, wherein said store comprises at least one strip housinga row of tools arranged along a line parallel to said crosspiece, saidtransfer device comprising a shuttle movable selectively between anumber of locations associated with said row and a group ofcorresponding locations in said stations.
 2. A system as claimed inclaim 1, wherein each of said stations comprises a container housingsaid number of tools oriented parallel to the tools in said strip.
 3. Asystem as claimed in claim 1, wherein said shuttle is carried by alinear actuator, and comprises a gripper for gripping the tool, saidgripper being movable, on said shuttle, parallel to said tools in saidstrip.
 4. A system as claimed in claim 3, wherein said store comprises anumber of rows of tools, actuating means being provided to move saidstore to select the row of tools from which to withdraw a tool by meansof said gripper.
 5. A system as claimed in claim 4, wherein said storecomprises a drum rotating on a shaft parallel to said crosspiece,wherein said drum houses a number of strips of tools in respectiveangular locations, and said actuating means selectively rotating saiddrum to position one of said strips corresponding to said gripper.
 6. Asystem as claimed in claim 5, wherein said gripper opens in a planeperpendicular to the axis of said shaft.
 7. A system as claimed in claim2, wherein said changing means comprise, for each of said heads, afurther gripper located on a worktable and movable vertically, saidcontainer being located on a support which is rotated to orient thetools inside the container parallel to the axis of the spindle of thecorresponding head.
 8. A system as claimed in claim 7, wherein saidcontainer also slides along said support parallel to said crosspiece, anappendix, integral with said head, engaging said container to move thecontainer along said support.
 9. A system as claimed in claim 8, whereinsaid container is maintained in a given position by elastic means, saidappendix moving said container, each time and in opposition to saidelastic means, from said given position to a position corresponding withthe tool to be changed.
 10. A system as claimed in claim 9, wherein saidelastic means comprise a spring for holding said container against astop on said support, said appendix engaging one end of said container.11. A system as claimed in claim 7, wherein said support comprises twoparallel guide elements for guiding said container, said appendix onlybeing engaged between said guide elements when the guide elements arerotated with the tools positioned parallel to said spindles.
 12. Asystem as claimed in claim 11, wherein said shuttle withdraws andinserts said tools horizontally inside each of said containers andinside the strips on said drum, said support being rotated 90°.
 13. Asystem as claimed in claim 1, wherein said machine comprises one row ofsaid machining heads and a control unit for coordinating said pluralityof changing means, wherein said tools are exchanged simultaneouslybetween each head and the respective intermediate stations by grippers.14. A tool-change system for a machine tool with a number of machiningheads for machining printed circuit boards, comprising:a common storefor housing tools for said heads, wherein said tools are transferredselectively between said store and a group of intermediate stations,changing means being provided to exchange a used tool on each head witha tool transferred to one of said stations, wherein said machinecomprises two rows of said machining heads on a common carriage, eachpair of corresponding heads in the two rows being associated with one ofsaid intermediate stations, and said tools being exchangedsimultaneously between said intermediate stations and the machiningheads by grippers.
 15. A system as claimed in claim 1, wherein each ofsaid heads comprises a respective sensor for detecting the condition ofthe tool, wherein said store is located outwards of two uprightssupporting said crosspiece; said shuttle being movable to an additionallocation outwards of said uprights and at a vessel for collectingrejected tools.